This invention is directed to a system for detecting and recognizing (distinguishing) an object in space from objects of similar characteristics (intensity, background noise, etc.) within the receiving aperture of video imaging devices. The system provides for detecting and/or identifying cyclic (periodic) modulation in video imagery of sufficient resolution to retrieve a positive signal to noise ratio.
The system of the present invention finds applications in such areas as searching for objects having emissions or transmissions of periodic variations such as those provided by pulsars in astronomical data such as data from the Hubble Space telescope. A second application of the system of the present invention is in the detection and location of beacons from downed aircraft or ships in trouble. Such detection and location functions being a necessary part of air, land, and sea rescue operations. A third applicaton of the system of the present invention is the detection, recognition and location of identificaton friend or foe (IFF) beacons from ground, sea, or air vehicles. Such IFF application could include specific temporal modulations whose signal to noise is enhanced by utilizing the principles of the present invention thus permitting a reduced amplitude beacon to help preserve covertnous of the vehicle from the opposing forces.
Apparatus and method of the system of the present invention has particular application to helicopters or other cyclic (rotary) modulation detection by providing means for improving discrimination against random noise.
A global application for the system described herein is in defense related functions such as the detection of enemy threats provided by air, land, or water vehicles and identifying these vehicles to determine if they are friends or foe.
While the system of the present invention finds application in many areas, as discussed supra, the principles of the present invention as set forth herein will be discussed specifically (as by way of example) in conjunction with the recognition and identification of helicopters. The system must first identify that its perceived target is a helicopter and then must identify the type of helicopter such as HIND, APACHE, etc. for appliction to the IFF processes.
Typically, detection and identification systems that use imaging or pseudo imaging techniques are based principally on spatial features of the target system rather than using temporal features. Such spatial systems tend to have very high false alarm rates and poor range performance for selection, recognition, and identification.
The system of the present invention uses the temporal signature of the helicopter to detect the helicopter and identify the type of helicopter. The temporal signature consisting of the helicopter rotor modulation is substantially unique to each type of helicopter and it produces a signal to noise ratio when filtered that is detectable and recognizable.
Previous work sponsored by the Government was limited to helicopter rotor modulation detection using the magnitude signal from a Fast Fourier Transform (FFT) filter. This work, using magnitude only was pursued to a point and a basic algorithm was defined.
Additional investigations by applicants have verified that the phase signal from the FFT filter contained intelligence relating to rotor modulation signature. The present invention describes means for using this intelligence from the phase signal to enhance the signal to noise ratio during the detection process and hence reduce the false alarm rate.
During later development work applicant demonstrated in a "proof of principle" procedure that the helicopter rotor modulation frequencies could be isolated beyond just a bin bandwidth capabilities of the FFT filter as was used in previous work to provide a detection/identification process.
It is, therefore, an object of the present invention to provide a system for visual detection of an object by visual imagery techniques.
It is further object of the present invention to provide such a system which is not only capable of such detection but also has the capability of recognizing and identifying such an object.
It is yet a further object of the present invention to provide such a system wherein the object is a helicopter.
It is still yet a further object of the present invention to provide such system with means to analyze the helicopter rotor modulation signal to determine or identify such helicopter for application to IFF.